1. Field of the Invention
The present invention relates to a rack and pinion steering gear for road vehicles.
2. Description of the Prior Art
A prior art rack and pinion steering gear, as exemplarily shown in FIG. 7, includes a pinion 1 adapted to be driven by a steering wheel and a rack 2 meshing the pinion 1 for movement in the longitudinal direction by being driven by the pinion 1. The rack 2 is connected at the opposite ends to dirigible wheels by way of a steering linkage so that longitudinal movement of the rack 2 causes rotation of the dirigible wheels.
In operation, the rack tends to flex or move away from the pinion 1 in transmission of steering efforts therebetween, thus reducing the contact ratio. In order to prevent such movement of the rack 2, a retainer 3 is provided for urging the rack 2 against the pinion 1 under the bias of a coil spring 4. The preload applied from the spring 4 to the rack 2 is adjusted to a suitable value through adjustment of the screwed amount of an adjuster 5.
In the above arrangement, the rack 2 is caused to vibrate in its longitudinal direction due to "kick back" of the dirigible wheels during movement of the vehicle over a rough road. This causes the rack 2 to flex away from the pinion 1 which is held stationary by the driver and allows the retainer 3 to strike against the adjuster 5 to produce a striking sound which is so-called a rattling sound.
In order to solve this problem, it has been proposed to interpose a resilient member (usually, Belleville spring) 6 between the adjacent end faces 3a, 5a of the retainer 3 and the adjuster 5, as disclosed in Japanese Utility Model Publication Nos. 59-133364 and 58-142179.
However, with the above arrangement, the resilient member (Belleville spring) 6 is pressed into a completely flat shape as shown in FIG. 8 when the retainer 3 comes nearest possible to the adjuster 5, thus subjecting the resilient member 6 to an excessively large load.
For this reason, in case of a vehicle of the kind frequently used for movement over a rough road, the durability of the resilient member 6 is a great problem. However, when the spring 4 is designed by giving the durability priority over the spring constant, the adjustable range of the preload becomes too narrow to obtain a desired performance of the steering gear or another problem arises that a rattling sound preventing action is not attained.